1. Field of the Invention
This invention relates to an ophthalmic measuring apparatus, and more particularly to an ophthalmic measuring apparatus for detecting ophthalmic diseases in which laser light is radiated via an optical system at one spot in the eye, particularly in the anterior chamber thereof, and the laser light scattered therefrom is analyzed to measure the ophthalmic diseases.
2. Description of the Prior Art
The measurement of protein concentration in the anterior chamber of the eye is of great importance in determining whether the eye is inflamed, that is, whether a blood-aqueous barrier functions normally or not. Conventionally, a slit lamp microscope is very often used to determine the turbidity by grading via the naked eye. On the other hand, a photographic measuring method has been developed to make a quantitative measurement.
The determination by naked eye depends upon an examiner and is not reliable in data. To overcome this problem, a method has been proposed in which a laser beam is radiated in the eye and the light scattered therefrom is received and analyzed quantitatively (see, for example, U.S. Pat. No. 4,711,542).
In such a measuring method, the scattered or diffused light from portions in the eye such as the cornea, iris, crystalline lens, artificial crystalline lens implanted after operation of cataract etc. enters as noise into the laser beam scattered from the eye or into the measured spot in the eye in receiving the laser beam scattered. This degrades measurement accuracy and reduces the reproducibility of measured values.
To reduce the noise due to the reflected or scattered light entering into the spot to be measured in the eye, the Japanese Laid-open Patent Publication No. 135128/88 or U.S. Pat. No. 4,832,043 discloses an apparatus in which a laser beam is deflected for scanning in the eye beyond the width of a slit on a mask disposed in front of the photoelectric converter. The output signal (including noise components) obtained when the laser beam is deflected beyond the slit width is subtracted from the output signal (including effective and noise components) when the laser beam passes across the slit width, thereby removing background noise from the cornea, crystalline and so on.
In another method, the mask is displaced to measure the quantity of light obtained when the laser beam is located at upper and lower portions of the mask. In the same manner, the subtraction from the laser-scattered light is performed to remove the background noise.
The utilization of such methods in the prior arts makes it possible to remove noise based on the dark current in the photoelectric converter or unnecessary scattered or reflected light contained in the signal from the photoelectric converter, thus providing an improved resolving power and improved accuracy of measurement.
In the first method, however, means for deflecting the laser beam are required, while needing means for displacing the mask in the second method. This disadvantageously makes the apparatus complicated and expensive. Furthermore, these methods necessitate moving parts, which eventually may degrade the reproducibility of measured data and guarantee no precise measurement of data with high accuracy.